The present invention relates to heat exchangers, and more particularly air-to-air heat exchangers.
It is often desirable to transfer the heat from a relatively warm air mass to a relatively cool air mass. It is also often desirable to prevent the two masses of air from intermixing during such transfer, such as where one of the masses is relatively dirty or contaminated. A variety of air-to-air heat exchangers has been developed for conveying two air masses past one another to effect the heat transfer. Often the heat exchangers include a housing and a core unit removably mounted within the housing. The core may be periodically removed from the housing and cleaned as necessary to keep the heat transferring surfaces clean. Preferably, both the housing and the removable core are fabricated of plastic or polymeric materials to reduce corrosion problems associated with contaminated air masses flowing through the exchanger.
However, known heat exchangers are not without their drawbacks. Firstly, the housings are typically specialized constructions requiring a relatively large number of parts. Accordingly, assembly costs are high because the manufacturer must make and inventory all of these parts for assembly of the units. Additionally, a large stock of replacement parts must be maintained for subsequent servicing of the units.
Secondly, the core units of the heat exchangers are also difficult and expensive to manufacture. Although heat exchanger cores have been made of plastic, known methods of assembling these cores are time-consuming and expensive. In one construction, the adjacent tubes within the core unit are fused together under heat and pressure. An example of this method of construction may be seen in U.S. Pat. No. 3,616,022, entitled METHOD OF MAKING HEAT EXCHANGE COMPONENTS and issued Oct. 26, 1971, to Withers; and U.S. Pat. No. 3,537,935, entitled APPARATUS FOR MANUFACTURING A HEAT EXCHANGER COMPONENT FORMED WITH FLEXIBLE PLASTIC TUBES and issued Nov. 3, 1970, to Withers. This method of assembly must be carefully controlled at the proper temperature and pressure to prevent spoiling the core unit during manufacture. Additionally, the method restricts air flow between and around the heat transfer tubes. In another construction, the tubes are fused to one another by inserting hot mandrels into adjacent tubes to soften and expand the tubes into fusing engagement with one another. An example of this construction may be seen in U.S. Pat. No. 2,433,546, entitled METHOD AND APPARATUS FOR FORMING PLASTIC RADIATOR CORES and issued Dec. 30, 1947, to Cornelius. However, in this method also, the temperature of the mandrels must be very carefully controlled to prevent excessive or inadequate softening of the ends of the heat exchange tubes during the fusing operation. If not carefully controlled, the tubes of the core are excessively or inadequately fused. Proper alignment of tube ends, one with the others, is also difficult in known manufacturing methods. Additionally, although it is desirable to use dissimilar materials (e.g., Teflon, nylon, polyethylene, polypropylene, and most crystalline polymers) in fabricating separate elements of the core unit to maximize anticorrosive properties while minimizing cost, suitable adhesives for such dissimilar materials are expensive or simply unavailable; and consequently such dissimilar materials cannot be used.